build-tools: copy the removed site.py from setuptools

Fixes python programs (like meson) from using libraries from incorrect
places.

Upstream reference: pypa/setuptools#2295

Fixes: https://gitlab.freedesktop.org/gstreamer/cerbero/-/issues/307
Part-of: <https://gitlab.freedesktop.org/gstreamer/cerbero/-/merge_requests/655>

Author: ystreet

cerbero/bootstrap/build_tools.py

@@ -17,15 +17,19 @@
 # Boston, MA 02111-1307, USA.
 
 import os
+import sysconfig
+import shutil
 
 from cerbero.config import Config, Platform, DistroVersion
 from cerbero.bootstrap import BootstrapperBase
 from cerbero.build.oven import Oven
 from cerbero.build.cookbook import CookBook
 from cerbero.commands.fetch import Fetch
 from cerbero.utils import _, shell
+from cerbero.utils import messages as m
 from cerbero.errors import FatalError, ConfigurationError
 
+from pathlib import PurePath
 
 class BuildTools (BootstrapperBase, Fetch):
 
@@ -120,8 +124,36 @@ def _setup_env(self):
         self.recipes = self.BUILD_TOOLS
         self.recipes += self.PLAT_BUILD_TOOLS.get(self.config.platform, [])
 
-    def start(self):
+    def insert_python_site(self):
+        try:
+            import setuptools.version as stv
+        except ImportError:
+            return
+
+        version = [int(v) for v in stv.__version__.split('.')]
+        if len(version) < 1 or version[:1] < [49]:
+            return
+
+        m.warning('detected setuptools >= 49.0.0, installing fallback site.py file. '
+            'See https://github.com/pypa/setuptools/issues/2295')
+
+        # Since python-setuptools 49.0.0, site.py is not installed by
+        # easy_install/setup.py anymore which breaks python installs outside
+        # the system prefix.
+        # https://github.com/pypa/setuptools/issues/2295
+        #
+        # Install the previously installed site.py ourselves as a workaround
+        config = self.cookbook.get_config()
+
+        py_prefix = sysconfig.get_path('purelib', vars={'base': ''})
+        # Must strip \/ to ensure that the path is relative
+        py_prefix = PurePath(config.prefix) / PurePath(py_prefix.strip('\\/'))
+        src_file = os.path.join(os.path.dirname(__file__), 'site-patch.py')
+        shutil.copy(src_file, py_prefix / 'site.py')
+
+    def start(self, jobs=0):
         self._setup_env()
+        self.insert_python_site()
         # Check build tools at the last minute because we may have installed them
         # in system bootstrap
         self.recipes += self.check_build_tools()

cerbero/bootstrap/site-patch.py

@@ -0,0 +1,78 @@
+# Originally kept from https://github.com/pypa/setuptools/pull/2166/files
+
+def __boot():
+    import sys
+    import os
+    PYTHONPATH = os.environ.get('PYTHONPATH')
+    if PYTHONPATH is None or (sys.platform == 'win32' and not PYTHONPATH):
+        PYTHONPATH = []
+    else:
+        PYTHONPATH = PYTHONPATH.split(os.pathsep)
+
+    pic = getattr(sys, 'path_importer_cache', {})
+    stdpath = sys.path[len(PYTHONPATH):]
+    mydir = os.path.dirname(__file__)
+
+    for item in stdpath:
+        if item == mydir or not item:
+            continue  # skip if current dir. on Windows, or my own directory
+        importer = pic.get(item)
+        if importer is not None:
+            loader = importer.find_module('site')
+            if loader is not None:
+                # This should actually reload the current module
+                loader.load_module('site')
+                break
+        else:
+            try:
+                import imp  # Avoid import loop in Python 3
+                stream, path, descr = imp.find_module('site', [item])
+            except ImportError:
+                continue
+            if stream is None:
+                continue
+            try:
+                # This should actually reload the current module
+                imp.load_module('site', stream, path, descr)
+            finally:
+                stream.close()
+            break
+    else:
+        raise ImportError("Couldn't find the real 'site' module")
+
+    # 2.2 comp
+    known_paths = dict([(
+        makepath(item)[1], 1) for item in sys.path])  # noqa
+
+    oldpos = getattr(sys, '__egginsert', 0)  # save old insertion position
+    sys.__egginsert = 0  # and reset the current one
+
+    for item in PYTHONPATH:
+        addsitedir(item)  # noqa
+
+    sys.__egginsert += oldpos  # restore effective old position
+
+    d, nd = makepath(stdpath[0])  # noqa
+    insert_at = None
+    new_path = []
+
+    for item in sys.path:
+        p, np = makepath(item)  # noqa
+
+        if np == nd and insert_at is None:
+            # We've hit the first 'system' path entry, so added entries go here
+            insert_at = len(new_path)
+
+        if np in known_paths or insert_at is None:
+            new_path.append(item)
+        else:
+            # new path after the insert point, back-insert it
+            new_path.insert(insert_at, item)
+            insert_at += 1
+
+    sys.path[:] = new_path
+
+
+if __name__ == 'site':
+    __boot()
+    del __boot